HP 2000s Guia do Utilizador descarregar pdf (Página 51)

Storage Management Overview

51NAS 2000s Administration Guide

Advantages

Distributed data guarding offers:

■ High read and write performance

■ Protection against data loss if one drive fails

■ Increased usable storage capacity, since capacity equal to only one physical drive is used

to store parity information

Disadvantages

Some disadvantages of distributed data guarding are:

■ Lower write performance than RAID 0 or RAID 1+0

■ Possibility of data loss if a second drive fails before data from the first failed drive has

been rebuilt

RAID ADG—Advanced Data Guarding

RAID ADG is similar to RAID 5 in that parity information is generated (and stored) to protect

against data loss caused by drive failure. With RAID ADG, however, two different sets of

parity data are used. This allows data to still be preserved if two drives fail. As can be seen

from Figure 26, each set of parity data uses up a capacity equivalent to that of one of the

constituent drives, for a total parity usage of two drives of space.

This method is most useful when data loss is unacceptable, but cost must also be minimized.

The probability that data loss will occur when configured with RAID ADG is less than when

configured with RAID 5.

Note: The ADG feature is available only with the optional Smart Array 5304/6404 Controller

installed.

Figure 26: RAID ADG (advanced data guarding) with two sets of parity data

Advanced Data Guarding technology offers the best combination of fault tolerance and usable

disk space among RAID levels.

P5,6

Q7,8

P3,4

Q5,6

P1,2

Q3,4

P7,8

Q1,2

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HP 2000s Guia do Utilizador Página 51